Method of evaluating stretch-flangeability with small-scale specimen without specimen size effects

Abstract

A method according to the present invention, it is possible to accurately measure the stretch-flangeability of sheet metal materials without size effects even when a small amount of specimen is used, compared with the stretch-flangeability established as an international standard, and to measure the stretch-flangeability in the local region. The method according to the present invention includes (a) performing a computer simulation of a small-scale specimen having a predetermined size by using finite element analysis to determine a size of the small-scale specimen; (b) using a standard-scale specimen having the same material as the small-scale specimen specified in the step (a) to perform a punching process specified in the standard testing method; (c) observing a distribution pattern of shearing defects in a hole-edge region of the specimen having performed the punching process, and evaluating a hole expansion ratio; (d) comparing the hole expansion ratio and the distribution pattern of shearing defects between the small-scale specimen and the standard-scale specimen to verify measurement reliability for the stretch-flangeability of the small-scale specimen; and (e) using the size of the small-scale specimen having verified the measurement reliability to evaluate stretch-flangeability.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention[0001]The present invention relates to a method of evaluating an accurate stretch-flangeability of a sheet metal material with a small-scale specimen. Specifically, the present invention relates to a method of evaluating stretch-flangeability of obtaining the same value as in the measurement of using a standard-scale specimen without the specimen size effects which are an important factor in the formability test and differ in formability evaluation result depending on a specimen size, even when the specimen size is reduced as compared with the standard-scale specimen in the hole expansion test which is the ISO 16630 international standard stretch-flangeability evaluation method.2. Description of the Related Art[0002]To prepare the trend towards more demanding environmental and safety regulations worldwide, the automobile industry has continued to reduce the weight of body-in-white components and to increase their stability by using...

AI Technical Summary

Benefits of technology

Enables reliable and economical evaluation of stretch-flangeability using a small-scale specimen, reducing material usage and accelerating the evaluation process, while maintaining accuracy comparable to standard-scale specimens, thus facilitating rapid and effective assessment of advanced high-strength steel sheets.

Problems solved by technology

However, in the case of the standard evaluation method, an excessively large-sized specimen is required in comparison with evaluation methods for other mechanical properties, so that there is a disadvantage in that the stretch-flangeability of steel in the development stage in which a sheet steel is not mass produced and the local stretch-flangeability of the sheet material may not be measured.

In addition, due to the standard evaluation method of requiring a large-sized specimen for the stretch-flangeability evaluation, it may take a long time for evaluation and feedback of the stretch-flangeability in development of advanced high-strength steel sheets to be applied to automobile components.

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